1. Technical Field
This disclosure generally relates to well cementing. More specifically, the disclosure relates to a methodology for designing a cement composition and an apparatus used therein.
2. Background
Zonal isolation refers to the isolation of a subterranean formation or zone, which serves as a source of a natural resource such as gas, oil, or water, from other subterranean formations. To achieve isolation of a subterranean formation, a well bore is typically drilled down to the subterranean formation while circulating a drilling fluid through the wellbore. After the drilling is terminated, a string of pipe, e.g., casing, is run in the wellbore. Next, primary cementing is typically performed whereby a cement slurry is placed in the annulus and permitted to set into a hard mass, thereby attaching the string of pipe to the walls of the wellbore and sealing the annulus. Subsequent secondary cementing operations such as squeeze cementing may also be performed.
Generally, cement slurry design for oil field applications involves optimizing slurry density, rheology, pump time, fluid loss, settling, strength development time, gas migration during placement, and mechanical properties such as compressive strengths, tensile strength, Poisson's ratio, Young's modulus, etc. for long-term zonal isolation. These mechanical properties may be modified by the inclusion of various additives with varying densities. One challenge to the inclusion of such additives is the effect of density variations of the additives on the homogeneity of the slurry. The differing densities of additives may result in a non-uniform density distribution in the slurry. For example, higher density additives may tend to settle to the lower portion of the slurry while lower density additives tend to rise to or remain in the upper portion.
A conventional method of determining settling is performed on set cement. However, such procedure takes time since the cement has to be cured and set prior to settling measurements, which may take up to 14 days. Thus, it would be desirable to develop an improved methodology for determining settling. It would also be desirable to develop a methodology for designing a cement composition that is suitable for long-term zonal isolation in a subterranean formation.